The objectives of this project are (a) to elucidate the role of prolactin in the inhibition of sexual behavior in the male rat; (b) to study the regulation of spontaneous ejaculation; and (c) elucidate inhibitory effects on sex behavior antihypertensive and psychotropic drugs, with particular reference to the possible involvement of prolactin and of ejaculatory inhibition. The approach utilized will involve experimental production of hyperprolactinemia in rats and the correlation of behavioral changes with circulating prolactin, luteinizing hormone and testosterone. Possible mechanisms of prolactin-induced behavioral inhibition which will be investigated include: suppression of luteinizing hormone releasing hormone (LHRH); inhibition of testicular androgen production or sensitivity and activation of the endogenous opiate system. In studying behavioral inhibition, individual tests will be performed to identify specific effects on arousal and the erection and ejaculation reflexes as well as on mating behavior as a whole. In connection with this aim we will study hormonal and neural determinants of spontaneous ejaculation as well as the respective roles of light-controlled diurnal rhythms in this and the erectile reflex system. Finally, the possibility that prolactin has a significant effect on female sexual behavior will be investigated.